The goal of this work is to develop a diagnostic immunoassay for breast cancer using antibodies produced in response to a growth inhibitory factor (GIF) isolated from human plasma derived serum (PDS). In addition to heterologous antisera from rabbits, we will explore the production of monoclonal antibodies by hybridomas. The specific plan of attack includes: 1) The purification of antibodies produced against GIF and measurement of antibody yield by indirect enzyme linked immunosorbent assay (ELISA), 2) Quantitation of the amount of GIF in PDS samples from several population groups using both rabbit and monoclonal antibodies in a double antibody method of ELISA for antigen detection. The basis for pursuing this project stems from ongoing experiments which show in a biological assay with MCF-7 that PDS samples express growth inhibitory activity which varies among population groups but is absent or diminished in breast cancer patients. In addition, only mammary cells in primary culture or lines derived from malignant tumors are growth inhibited by PDS while the growth of cells from normal tissue sources is not inhibited. These results led to the hypothesis that the level of inhibitory factor in serum can be correlated with the presence or absence of breast cancer.